How to check if a method was implemented in class Delphi - delphi

Question

I need to check if method was implemented in class.
My classes implements an interface.
Code.
IMyInterface = interface
['{538C19EB-22E3-478D-B163-741D6BB29991}']
procedure Show();
end;
TMyClassFormCustomer = class(TInterfacedObject, IMyInterface)
public
procedure Show();
end;
TMyClassFormVendors = class(TInterfacedObject, IMyInterface)
public
procedure Show();
end;
....
procedure TMyClassFormCustomer.Show;
var
Form: TFormCustomer;
begin
Form:= TFormCustomer.Create(nil);
try
Form.ShowModal();
finally
FreeAndNil(Form)
end;
end;
{ TMyClassFormVendors }
procedure TMyClassFormVendors.Show;
begin
end;
It is possible to check if method TMyClassFormVendors.Show have implementation?
When a method not have implementation I have disable item in menu
Thanks.

Answer 1

I see a couple of possibilities:
If your TMyClassFormVendors does not want to do anything in .Show then simply don't declare and implement IMyInterface. In your code you can then query for that interface with if Supports(MyClass, IMyInterface) and react accordingly (Disable Menu entry)
If your IMyInterface interface actually has more than one method declared, some of which are supported (I don't want to use the word implemented, as all methods have to be implemented) and others are not, then you should better split the interface into several different ones and proceed as described in 1
You could also declare and implement another interface "ICapabilities" that could have methods like CanShow etc. In your code you could then query your class like if (Myclass as ICapabilities).CanShow then ...
I personally would favour 2. as it is the cleanest approach IMO, but it depends on what you want to do specifically

Answer 2

You could use similar approach as it is used for handling the event methods. So what you want to do is instead of implementing the method directly into your class you add a property which can store a method pointer to the actual method you wanna use. And then at runtime you only check to see if the pointer to such method was already assigned or not.
The code for this would look something like this:
type
//Method type object
TMyMethod = procedure (SomeParameter: Integer) of object;
TMyClass = class(TObject)
private
//Field storing pointer to the method object
FMyMethod: TMyMethod;
protected
...
public
//proerty used for assigning and accesing the method
property MyMethod: TMyMethod read FMyMethod write FMyMethod;
end;
When you are designing the method objects you can define how many and which type of parameters you wanna use in that method.
Don't forget you need to assign method to your method property in order to use it. You can do this at any time. You can even unassign it by setting it to nil if needed.
You do this in same way as you do with event methods
MyClass.MyMethod := MyProcedure;
where MyProcedure needs to have the same parameter structure as the method object type you defined earlier.
And finally you can check to see if methods has been assigned at runtime using:
if Assigned(MyClass.MyMethod) then
begin
//Do something
end
else //Skip forward
EDIT: Another advantage of this approach is that your actual method that you use can be defined and written in completely different unit.